1. Field of the Invention
The present invention relates to a multilayer wiring board. More particularly, the present invention relates to a multilayer wiring board inside which a condenser structure is composed and also relates to a method of manufacturing the multilayer wiring board. Further, the present invention relates to a semiconductor device into which the multilayer wiring board is incorporated and also relates to a method of manufacturing the semiconductor device.
2. Description of the Related Art
Recently, the density of electronic equipment has been highly increased. Accordingly, a multilayer wiring board in which a plurality of wiring layers are laminated together has been realized. A multilayer wiring board of the prior art is shown in FIG. 6.
The multilayer wiring board 201 of the prior art, shown in FIG. 6, includes a core base material 202 made of insulating material such as glass-epoxy resin or ceramics. On both sides of the core base material 202, there are provided a plurality of wiring layers 203, 203, . . . and a plurality of interlayer insulating layers 204, 204, . . . which are alternately laminated on each other. In this structure, the core base material 202 is provided for enhancing the mechanical strength of the entire multilayer wiring board 201 and also for enhancing the workability of the multilayer wiring board 201.
In this core base material 202, there are provided through-holes 202a, 202a, . . . . On the inner walls of these through-holes 202a, 202a, . . . , there are provided copper plating layers. Due to these copper plating layers, the wiring layers 203, 203 provided on both sides of the core base material can be electrically connected to each other.
Although not shown in FIG. 6, among these wiring layers 203, 203, . . . , there are provided an electric power supply layer for supplying electric power to the semiconductor element 206 to be mounted and a signal layer for inputting and outputting a signal to and from the semiconductor element 206.
On this multilayer wiring board 201 of the prior art, the semiconductor element 206 is mounted via the solder bumps 207. A semiconductor device, in which the semiconductor element 206 is mounted on the multilayer wiring board 201, is mounted on a board (not shown) such as a mother board via the solder bumps 205.
In this connection, it is common that a chip condenser (not shown) for decoupling is mounted on the multilayer wiring board 201 so that fluctuation in electric potential of the electric power supply layer, and the cross talk caused between the signal layers, can be reduced. Both electrodes of this chip condenser are respectively connected with the wiring layers to be decoupled. In this case, it is preferable that the length of the wiring between the chip condenser and the wiring layer is as short as possible. The reason is that when the length of the wiring between the chip condenser and the wiring layer is long, the impedance is increased, so that it becomes difficult for the chip condenser to accomplish the above object. Especially when the drive rate of the semiconductor element 206 is increased, the impedance is remarkably increased. Therefore, it becomes impossible to increase the operation rate of the semiconductor device composed of the multilayer wiring board 201 and the semiconductor element 206.
From the above viewpoint, it is conventional practice that the chip condenser is embedded in the interlayer insulating layer 204 so that the length of the wiring between the chip condenser and the wiring layer 203 can be reduced.
However, when the chip condenser is embedded in the interlayer insulating layer 204 as described above, it becomes necessary that the film thickness of the interlayer insulating layer 204 is larger than the thickness of the chip condenser. Therefore, it becomes impossible to reduce the film thickness of the interlayer insulating layer. When the film thickness of the interlayer insulating layer is large, it is impossible to fulfill the recent requirements that the total thickness of the multilayer wiring board 201 should be reduced so as to provide a semiconductor device of high density. Further, when the film thickness is large, the cost of the interlayer insulating layer 204 is raised. Therefore, the manufacturing cost of the multilayer wiring board 201 is increased.
Further, irregularities corresponding to the profile of the chip condenser are formed on the surface of the interlayer insulating layer 204. Therefore, it is impossible to manufacture a multilayer wiring board 201, the surface of which is flat.
The present invention has been accomplished to solve the above problems.
It is an object of the present invention to provide a multilayer wiring board inside which a condenser structure is composed so that it unnecessary to provide a chip condenser in the multilayer wiring board.
According to the present invention, there is provided a multilayer wiring board comprising: a metal substrate as a core; a condenser dielectric layer formed to cover the metal layer; and a condenser electrode metal layer formed to cover the condenser dielectric layer, so that a condenser is defined by the metal substrate, the condenser dielectric layer and the condenser electrode metal layer.
According to the multilayer wiring board of the present invention, the multilayer wiring board includes a metallic base material (metal substrate) which composes a core. The surface of this metallic base material is covered with a dielectric layer for a condenser. Further, the surface of this dielectric layer for a condenser is covered with a metallic layer for a condenser electrode.
The metallic base material, the dielectric layer for a condenser and the metallic layer for a condenser electrode compose a condenser. That is, the metallic base material and the metallic layer for a condenser electrode function as both electrode plates of the condenser, and the dielectric layer for a condenser functions as a dielectric member interposed between them.
The condenser dielectric layer is provided with a first contact hole to communicate with the metal substrate.
The condenser electrode metal layer is provided with a second contact hole to communicate with the first contact hole, the diameter of the second contact hole being larger than that of the first contact hole. An insulating layer is formed on said condenser electrode metal layer and is provided with a via hole to communicate with the metal substrate through the second and first contact holes. A metal substrate contact metal layer is formed on an inner wall of the via hole, so that the metal substrate contact metal layer comes into electrical contact with the metal substrate.
According to such a multilayer wiring board of the present invention, the first contact hole communicating with the metallic base material is formed on the condenser dielectric layer. The second contact hole communicating with the first contact hole, the diameter of the second contact hole being larger than that of the first contact hole, is formed on the metallic layer for a condenser electrode.
According to the above structure, the side wall of the second contact hole and the surface of the metallic base material exposed to the bottom of the first contact hole are separate from each other by the peripheral edge section of the first contact hole. Therefore, even when foreign objects such as particles enter the first and the second contact holes, it is difficult for the metallic layer for a condenser and the metallic base material to be short-circuited with each other. Therefore, the reliability of insulation between the metallic layer for a condenser electrode and the metallic base material can be enhanced.
The condenser dielectric layer is an oxidized layer of a surface of the metal substrate. The metal layer is made of aluminum (Al) and the condenser dielectric layer is made of aluminum oxide. Otherwise, the metal layer can be made of titanium (Ti) and the condenser dielectric layer can be made of titanium oxide.
According to another aspect of the present invention, there is provided a method for manufacturing a multiplayer wiring board, the method comprising the steps of forming a dielectric layer on a surface of a metal substrate as a core and forming a condenser electrode metal layer to cover the condenser dielectric layer, so that a condenser is defined by said metal substrate, the condenser dielectric layer and the condenser electrode metal layer.
According to still another aspect of the present invention, there is provided a method for manufacturing a multilayer wiring board, said method comprising the following steps of: forming a dielectric layer on a surface of a metal substrate as a core; forming a condenser electrode metal layer to cover the condenser dielectric layer; providing the condenser electrode metal layer with a second contact hole; providing the condenser dielectric layer at an area in the second contact hole with a first contact hole to communicate with the metal substrate, the diameter of the first contact hole being smaller than that of the second contact hole; forming an insulating layer on the condenser electrode metal layer; providing the insulating layer with a via hole to communicate with the metal substrate through the second and first contact holes; and forming a metal substrate contact metal layer on an inner wall of the via hole, so that the metal substrate contact metal layer comes into electrical contact with the metal substrate.